Tone your lower body and core with this high-intensity interval training (HIIT) workout. You'll be challenged with 40 seconds of hard exercise followed by 20 seconds of recovery in between; these interval blocks will allow your body to enter a state of excess post-exercise oxygen consumption or EPOC, which is when you continue to burn calories even after your workout is over. (One of the reasons HIIT is basically the most effective workout there is.)

Los Angeles-based trainer Dana McCaw crafted this HIIT workout to torch both your lower body and your core. She'll lead you through a five-minute warm-up and two rounds of HIIT moves—the first to blast your lower body and the second to target your core.

How it works: you'll need a small ball or a towel. Follow McCaw through the warm-up and HIIT rounds, then cool down with some static stretches.

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